The present invention generally relates to a method of modeling dynamic characteristics of flight vehicles. Specifically, the present invention relates to a method of compiling input data defining characteristics of a flight vehicle and generating system output data for performing simulation, analysis, and design on the flight vehicle control system.
Existing methods of modeling high order flight vehicle dynamics and generating an output file for use in simulation, analysis, and design of flight vehicle controls are complicated and time consuming. The performance quality of flight vehicles, such as launch vehicles, re-entry vehicles, and high performance aircraft, is generally studied in two distinct, though related, phases. The first one deals with orbital mechanics, vehicle guidance, and the shaping of point mass trajectories assuming that the vehicle can be perfectly steered along the desired path. This analysis is usually referred to as “long period dynamics.” The second study deals with small variations or perturbations of the vehicle from its nominal trajectory. The perturbation dynamics have a shorter period and they are also referred to as “short period dynamics.” Flight vehicles are modeled as linear state-space representations used for analyzing the flight control system stability and performance with respect to guidance commands, wind gust disturbances, failures, etc.
Although vehicle parameters such as mass properties, aero data, trajectory, and others are constantly changing throughout a mission, flight control system (FCS) gains and filters are traditionally designed at fixed, mission critical flight conditions, called “time slices.” Critical conditions for rocket vehicles are at high dynamic pressures, lift-off, maximum slosh, before and after staging, high angles of attack (a), etc. The flight control system gains are interpolated or phased-in between the time slices using “gain scheduling.” For an aircraft one estimates the range of flight envelope in terms of alphas versus Mach number, and design flight control system gains at as many alpha and Mach number combinations as necessary to cover the flight envelope. Look-up tables of gains versus alphas and Mach numbers are coded in modeling software and the gains are interpolated at intermediate values.
There is a need for a modeling tool that can easily create vehicle state-space models for control design and analysis directly from vehicle parameters at different flight conditions, for flight vehicle models ranging from simple rigid-body models for preliminary flight control system design to more complex ones that include high order resonances used for detailed design, stability analysis and performance evaluation in presence of disturbances. The present invention is therefore motivated at least in part by the need for a comprehensive flight vehicle modeling tool that aggregates all input data and is easy and convenient to use and yet versatile enough to apply to different types of flight vehicles and varying parameters and complexity of modeling.